Security Researcher: Microsoft Downplaying IIS Vulnerability

A security researcher from nCircle says Microsoft is downplaying a vulnerability in its IIS (Internet Information Services) software.

Tyler Reguly, senior security engineer for nCircle, has accused Microsoft of gamesmanship in its description of the bug, noting Microsoft characterized it in separate ways.

For those who missed it, the vulnerability exists in the way the WebDAV extension improperly decodes a requested URL. The end result is that a successful exploit would allow a hacker to bypass authentication and gain unauthorized access to resources.

"Microsoft has classified this issue two different ways in two different places," he said. "On the SRD blog (it) refers to this as a Information Disclosure vulnerability, while the Microsoft Advisory refers to this as an elevation of privilege."

The point, he said, is that the bug should be called what it is--an access control breach or an authentication bypass. SRD acknowledges the Authentication Bypass but downplays it because you are accessing a single page with the anonymous user privileges, he added.

"Say you work for Company A and your company uses Company B to manage HR (including payroll)," he said. "Company B has a fairly basic web setup with a username/password in a separate directory for each customer. Once inside you have full access to the HR system."

"Now these are worst case scenarios, but in IS (information security) don't we always talk in worst case scenarios? Why should this be any different? This may not be the next Code Red but that doesn't mean we should disregard this and label it as elevation of privilege, which would imply some access already, existed or information disclosure, which to me implies no need to breach access controls."

Microsoft offered little in the way of a direct response to this, basically stating only that the company was unaware of any attacks and would continue to monitor the situation. US-CERT however has reported that hackers are actively exploiting the flaw.

In Microsoft's defense, there are a number of factors mitigating the vulnerability. As I mentioned here, only a specific configuration of IIS is vulnerable to attack, and the Windows Server 2003 IIS (version 6.0) does not have WebDAV enabled by default. While users await a patch, they can use URLScan to block malicious HTTP requests and consider changing filesystem ACLs to deny access to IUSR_[MachineName].